In recent, various manufacturers are active in a computer business and these manufacturers have been competing in developing computer technology. As a result, version upgrades to their computer programs and operating system programs have been made available in extremely short cycles. With the rapid popularization of the internet, these upgrades of the computer program and/or the operating system program are more frequently delivered or distributed over networks. Further, a data file has been greatly increased in data size due to enhanced features of application software, and meanwhile storage media of an enormous memory capacity such as DVD-RAM have been developed and put into use for storing these data files.
For version upgrade or installation of the application software or renewal of a file, in most cases is generally employed a technique of overwriting the version upgrade of such application software or a new file directly onto the original application software or the original file.
But the above conventional installation or renewal method inherently involves serious problems, as set forth below.
In the conventional method of overwriting the application software or the new file directly on the original software or file, when an unexpected error should occur while such overwriting operation of the upgrade or the new file is under process, the overwriting operation will not only be completed but also the original application software or file will be destroyed, and further data which have been created in a long time period will be lost instantly, and at the worst the operating system that has been running normally is brought to show awkward behavior or not to work in a normal manner.
Especially, should such unexpected error occur during upgrading operation of the operating system program, a fatal damage shall be invited in a computer system, resulting in destruction of the operating system program. Therefore, it is almost impossible for a user to recover from the unexpected trouble, since the computer system itself does not work at all. In such case, the user of the computer system often has to give up his (or her) created and accumulated data and is forced to initialize the computer system to install the operating system again. The above trouble has been left a long time to be solved quickly. In particular, with wide use of the network for distributing the computer programs, it is expected that opportunities will increase that communication errors shall occur during the course of overwriting operation of the program or data, and therefore it will be most important to solve the above mentioned troubles quickly.